I found this vendor online, and they offer GXL and TXL automotive grade wire in all kinds of sizes and color combinations, and in short lengths (down to 5 feet) to long lengths (over 1000 feet).
Their prices are very competitive, and they charged me NO SHIPPING or TAX on an $11.00 order of 25 feet of 14 gauge green.
They seem to ship fairly quickly, and delivery time from their midwest location to SoCal took about 3 to 4 workdays since it went USPS snail mail.

So if you are wiring up something custom, need specific size and color combo to match existing (they have lots of colors with stripes of varying colors) and can wait a week for it...this is a good source.

http://4rcustomswire.com